The parents of murdered schoolgirl Alice Gross are 'bewildered' after a coroner left a police file into their daughter's murder on a train.

An investigation has been launched after Chinyere Inyama, the senior west London coroner, lost the 30-page police file in November last year, a month after Alice's body was found in a London river.

Police tried to recover the file, which contained evidence against prime suspect Arnis Zalkalns, but concluded it had probably been "destroyed as waste".

An investigation is underway after a coroner lost a police file into the murder of Alice Gross

The Ministry of Justice is investigating the incident and why the file was ever taken from the coroner's office.

In a statement to The Mail On Sunday, Alice's parents, Ros Hodgkiss and Jose Gross, have expressed their frustration at the loss: "We have looked to the police and coroner to help us through our awful loss. Yet now we learn they [...] have withheld from us the loss of this terribly sensitive information about Alice.

‘We are extremely concerned, bewildered and angry – and we have asked for a full written explanation as to what exactly happened and why we were not told.’

Alice disappeared last August from her home in Hanwell, west London, sparking Scotland Yard's biggest search operation since the July 7, 2005, London bombings.

Arnis Zalkalns would have been charged over Alice's murder but killed himself days after her body was discovered

The 14-year-old's body was found weighted down in the Grand Union Canal in Ealing, west London, on September 30.

An inquest into Alice's death was opened and adjourned last October, but the coroner lost the vital document - given to him with preparations for the inquests into the deaths of Alice and Zalkalns - a month later.

A spokesman for the Metropolitan Police said it was informed by the coroner in November 2014 that he had "inadvertently disposed" of a document relating to the police evidence against Zalkalns.

The spokesman said an investigation to recover the document was undertaken and it was later concluded that it "was highly likely it had been destroyed as waste".

Details of the evidence against Zalkalns were given to the media in January with the agreement of the Crown Prosecution Service and the coroner.

Senior west London coroner Chinyere Inyama was said to have lost the 30-page police file in November last year while on a train

The Ministry of Justice said: "This clearly appears to be a troubling incident. A full investigation is now under way."

A full inquest into Alice's death is due to be held at the end of November or the beginning of December, and Mr Inyama has reserved judgment on whether it will be a jury inquest.

He is expected to hand down his ruling on the scope of the inquest in the next week.